The subject matter disclosed herein relates to fuel nozzles and more particularly relates to a fuel nozzle manifold having discrete passages in a single component.
The primary air polluting emissions usually produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide, and unburned hydrocarbons. It is well known in the art that oxidation of molecular nitrogen in air breathing engines is highly dependent upon the maximum hot gas temperature in the combustion system reaction zone. One method of controlling the temperature of the reaction zone of a heat engine combustor below the level at which thermal NOx is formed is to premix fuel and air to a lean mixture prior to combustion—often called a Dry Low Nox (DLN) combustion system. The thermal mass of the excess air present in the reaction zone of a lean premixed combustor absorbs heat and reduces the temperature rise of the products of combustion to a level where thermal NOx is significantly reduced. An example of a fuel nozzle that achieves a uniform fuel/air flow mixture through the user of a swirler is shown in FIG. 1.
FIG. 1 is a perspective view of a fuel nozzle 1 having an inlet flow conditioner 10 that provides most of the air for combustion of the nozzle. The inlet flow conditioner includes an annular flow passage 11 that is bounded by a solid cylindrical inner wall 12 at the inside diameter, a perforated cylindrical outer wall 13 at the outside diameter, and a perforated end cap 14 at the upstream end. In the center of the flow passage 11 is one or more annular turning vanes 15. Premixer air enters the inlet flow conditioner 10 from a high pressure plenum 21, which surrounds the entire assembly except the discharge end 35, through the perforations in the end cap 14 and cylindrical outer wall 13.
After combustion air exits the inlet flow conditioner 10, it enters the swirler assembly (sometimes called a swozzle assembly) 22. The swirler assembly 22 includes a hub 23 and a shroud 24 connected by a series of air foil shaped turning vanes, which impart swirl to the combustion air passing through the premixer. Each turning vane contains a first fluid supply passage 25 and a second fluid supply passage 26 through the core of the air foil. These fluid supply passages distribute fuel and/or air to first fuel injection holes (not shown) and second injection holes (also not shown), which penetrate the wall of the air foil. These fuel injection holes may be located on the pressure side, the suction side, or both sides of the turning vanes. Fuel enters the swirler assembly 22 through inlet ports 31 and annular passages 32, 33, which feed the fluid supply passages 25, 26 within the turning vanes. Fuel begins mixing with combustion air in the swirler assembly 22, and fuel/air mixing is completed in the annular passage 34. After exiting the annular passage 34, the fuel/air mixture enters the combustor reaction zone 35 where combustion takes place.
At the center of the nozzle assembly is a conventional diffusion flame fuel nozzle 41 having a slotted gas tip 42, which receives combustion air from an annular passage 43 and fuel through gas holes 44. The body of this fuel nozzle includes a bellows 45 to compensate for differential thermal expansions between this nozzle and the premixer.
The multiple concentric tube design of FIG. 1 typically used to transfer fuel and air in different circuits works fairly well for a few circuits, but gets difficult to package and ensure durability as the number of circuits increase. As a result, circuit designs become limited. Furthermore, due to the fluids flowing on either side of multiple thin concentric tubes making up most fuel nozzles, the metals of these tubes are at different metal temperatures. The differential temperatures of the separate metal tubes cause thermal strain at the tube connections, which are typically brazed. Axial strain is also a problem. While axial strain can be relieved by an expansion joint, such as a bellows or other suitable device, it adds cost to the nozzle and causes packaging restrictions. Radial strain of the thin metal tubes of a fuel nozzle is also a concern at nozzle design temperatures, but radial strain is typically difficult to mitigate.
While thin metal tubing does provide some bending stiffness, it is typically at risk for being driven at a bending resonance by the turbine within which the nozzle is used. Finally, the axial separation between the outlets of the fuel circuits can severely restrict the design of the joints separating the circuits. The resulting joint may compromise durability.